Humans can perceive five basic tastes: sweet, sour, bitter, salty and umami. In addition to these five basic tastes, researchers have identified an additional five tastes that humans can detect: fat, metallic, alkaline, astringent and spicy. Understanding the nuances of taste perception can help explain our attractions and aversions to certain foods and beverages. Let’s explore the 10 known tastes that humans can perceive.
Sweet
Sweet taste detects the presence of sugars and carbohydrates in foods. Sucrose, glucose and fructose are examples of sweet-tasting molecules. Sugars are a vital source of energy for the body, which may explain the appeal of sweet foods. The tongue’s taste buds have receptors that bind to sweet molecules, triggering signals to the brain. Sweetness tends to be most pronounced at the tip of the tongue.
Many processed and natural foods have added sugars to boost their sweet taste. Fruits are prized for their sweetness, which indicates ripeness. The sweet taste preference varies among individuals and declines with age in some people.
Sour
Sour taste detects the presence of acids, such as citric acid in lemons and acetic acid in vinegar. It provides a tart, sharp flavor. Sour taste receptors respond to the hydrogen ions (H+) of acids. Sourness is commonly perceived along the sides of the tongue.
In small amounts, sourness adds a pleasant zing and contrast to foods. But at high concentrations, sourness can cause us to pucker up and recoil. Fermented foods like yogurt, pickles and wine derive some of their appeal from sourness. Unripe fruits tend to be more sour than ripe ones.
Bitter
Bitter taste detects the presence of alkaloids and other potentially toxic compounds in plants, serving as an innate warning signal against poisoning. Bitter taste receptors appear to bind alkaloid molecules, triggering signals of unsuitability as food. Bitterness is often most acutely sensed at the back of the tongue.
Many beneficial plant compounds have a bitter taste, including caffeine in coffee, tannins in tea and phytochemicals in vegetables. While bitterness can be unappealing, people can acquire a taste for bitter foods, as seen with dark chocolate, coffee and leafy greens.
Salty
Salty taste detects the presence of sodium ions (Na+) and other mineral salts in foods. Saltiness provides a pure, elemental flavor. Salt receptors on the tongue trigger electrical signals to the brain. Saltiness is usually most prominent at the front sides of the tongue.
Sodium and other electrolyte minerals are vital for fluid balance and nerve transmission. Salt enhances and balances flavor profiles, which may explain its universal popularity as a seasoning. However, excess salt intake is linked with hypertension, making moderation important.
Umami
Umami taste detects the presence of amino acids like glutamate and nucleotides like inosinate in foods. Known as the “fifth taste,” it provides a savory, meaty, brothy flavor. Umami receptors respond to these molecules, signaling protein content to the brain. Umami is sensed across broad areas of the tongue.
Foods naturally high in umami compounds include aged cheese, meat, mushrooms and seaweed. Monosodium glutamate (MSG) is sometimes added to foods to amplify umami. The taste improves the palatability of meals and balances salty and sweet flavors.
Fat
Fat taste is the Sixth taste. It detects the presence of fatty acids in foods. Fat molecules may bind to receptors on taste buds, signaling high fat content. Fatty acid transporters may also absorb fat molecules, leading to activation of signaling cascades. Fat taste may register most intensely at the back of the tongue.
While fat contains more than twice the calories per gram as carbohydrates or protein, small amounts enhance flavor, texture and satisfaction. However, overconsumption of high-fat foods is a risk factor for obesity and heart disease. Understanding fat taste mechanisms could lead to the development of safe fat substitutes.
Metallic
Metallic taste is the Seventh taste. It detects metals ions in foods, especially iron, copper and zinc. The mechanism is not fully understood but may involve metal ions binding to receptors on taste buds. Metallic taste appears to register most intensely along the edges of the tongue.
The taste of blood is the prime example of metallic flavor. Iron supplements or steel cookware can also lend a metallic taste. For most people, it is not a desirable flavor. But heightened sensitivity to metallic taste is considered a risk factor for Parkinson’s disease.
Alkaline
Alkaline taste is the Eighth taste. It detects the presence of alkali chemicals, such as sodium bicarbonate (baking soda), producing a “soapy” flavor. Alkaline taste may function via taste bud receptors sensitive to pH changes or carbonate ions. It appears most sensitive at the back of the tongue.
Many cleaning products have an alkaline taste. Although not very appetizing, alkaline water has grown in popularity. A slightly alkaline taste can balance more acidic foods and drinks.
Astringent
Astringent taste is the Ninth taste. It detects the presence of tannins and polyphenols, compounds found in many plants. By binding proteins and contracting tissues, they produce a dry, puckering mouthfeel.
Tea, red wine and unripe fruit have high tannin levels and an astringent taste. Despite some harshness, a touch of astringency can be appealing, as seen with strong black tea. Astringency balances fatty and oily textures in foods and masks metallic tastes.
Spicy
Spicy taste, also known as pungency or hotness, is the Tenth taste. It detects certain volatile compounds, like capsaicin in chili peppers, that chemically activate nerve fibers causing a burning sensation. Although distinct from taste, this effect registers in the brain as spiciness or heat.
Spicy foods contain irritant compounds that are perceived as hot and painful, signaling potential damage. However, people develop tolerance to this effect. Capsaicin offers health benefits, providing spicy foods’ popularity despite their burn.
Conclusion
In summary, humans have receptors that enable the perception of 10 taste modalities: sweet, sour, bitter, salty, umami, fat, metallic, alkaline, astringent and spicy. Understanding taste mechanisms provides insight into nutrition, dining preferences and cooking techniques. The incredible diversity of flavors we can experience makes eating an adventure.